1. Field of the Invention
This invention relates to controlling the hydrolytic specificity of amylases by immobilization on a carrier and to the use of these immobilized enzymes in the preparation of retrogradation-resistant starches of reduced molecular linearity.
2. Description of the Prior Art
The stability of aqueous starch dispersions often determines their acceptance in many industrial and food applications. The extent of retrogradation of starch pastes is related inversely to temperature and directly to concentration. At room temperature, gelling or precipitation may readily occur in corn starch dispersions of moderate, e.g., 2%, concentration. It is generally recognized that amylose, the linear molecular component of starch, is chiefly responsible for this phenomenon. Consequently, starches that consist exclusively of branched amylopectin, such as those derived from waxy varieties of corn or sorghum grain, have been used where amylose crystallization, either during or after an application, is a disadvantage. The more costly waxy starches differ in rheological properties from ordinary starches having amylose contents in the range of 17-28%. Alternatives for preparing stable amylaceous dispersions have included use of amylopectin obtained by starch fractionation, chemical derivatives and modifications of starch (e.g., hydroxyethyl ether and oxidized starches) that minimize amylose retrogradation by blocking of hydrogen bonding sites, and codispersion of starches with fatty materials that complex with amylose.
In a related field, enzymic hydrolysis is a well-established technique in the art for degrading starch to short-chain saccharides as taught, for example, by Leach et al. in U.S. Pat. No. 3,922,196. Reports by J. F. Robyt et al. in Arch. Biochem. Biophys. 122: 8-16 (1967) and K. K. Tung et al., Anal. Biochem. 29: 84-90 (1969) teach that soluble alpha-amylase is characterized by endoenzymic activity and is nonselective in the degradation of the amylose and amylopectin components. It thereby cleaves polymeric starch into a product having a random distribution of molecular chain lengths and properties unlike those of the original components, amylose and amylopectin.